This invention relates to the conversion of wastes, and more particularly to the conversion of sludges having a high organic content and a significant proportion of ash, such as paper mill sludge.
Pulp and paper companies produce large quantities of processed waste known as sludges. Typically, these sludges have been disposed of by landfilling. Growing shortage of landfill space and more restrictive environmental regulations have made that method of disposal more costly and less desirable.
The sludge from a recycled paper process provides a greater problem of disposal than does the sludge from standard paper processes. Sludge from the recycling process contains a significant amount of fiber and paper coatings. The amount of sludge generated from the paper recycling process is more than the amount of sludge generated from virgin pulp. The advent of widespread paper recycling has resulted in an increase in the total quantity of sludge.
As an alternative to landfilling, paper mill sludge has been burned using fluidized bed boiler technology. Burning the sludge recovers its heat content, vaporizes the moisture content, and reduces the waste volume. However, because of the large ash content in paper mill sludge, there still remains a considerable waste product that requires disposal such as by landfilling.
Cyclone furnaces have been used for many years for burning coal to power boilers. A characteristic of cyclone furnaces is that they generate a slag which has a glassy consistency. The slag from coal-fired cyclone boilers is used as a construction material in roads, as an abrasive or grit, and in roofing products.
Although cyclone furnaces were developed to burn coal grades that were not well-suited for pulverized coal combustion, they have also been used to burn solid waste fuels as a supplemental fuel, or to burn fuel oils or gases as the primary, contingency, or start-up fuel. When waste fuels are used with coal, such supplemental fuel typically has a relatively low ash content and provides less than 20 percent of the heat input and a smaller percentage of the pounds per hour of fuel fed to the cyclone furnace.